Because an iron-based metallic material, particularly typified by carbon steel, has high strength and hardness, and is more inexpensive than other metal, it is most commonly used.
An iron-based metallic material is inferior to chrome, nickel, and cobalt in terms of corrosion resistance and heat resistance. Accordingly, an iron-based metallic material is likely to have a problem in durability due to the occurrence of rust or the growth of an oxide film.
For this reason, an iron-based metallic material that is coated with a resin or provided with a lining has generally been used.
However, to make the most of the heat resistance, abrasion resistance, and electrical conductivity (antistatic property) of iron itself, the problems of corrosion and abrasion resistance, and electrical conductivity and the like needed to be solved.
Meanwhile, stainless steel in which chrome, nickel or molybdenum and the like is alloyed has been commonly used in applications not amenable to a resin coating or a lining.
With resource prices rising in recent years, however, there are an increasing number of cases in which it is difficult to use these alloys, due to reasons of economy.
In addition to phosphate treatment, treatment using a chromic acid has been effective as conventional art for compensating for problems with corrosion resistance, heat resistance, adhesion, and the like in an iron-based metallic material.
In recent years, however, worldwide environmental regulations have made the use a chromic acid difficult.
In response to these circumstances, a method of performing a post-treatment of a phosphate coating, in which steel or a galvanized steel plate is dipped in a solution of a silane coupling agent after phosphate treatment in a step for phosphate treatment of a galvanized steel plate or steel was disclosed in Patent Document 1.
Additionally, Patent Document 2 discloses a metal surface treatment method of performing film chemical conversion using a phosphate aqueous solution on the surface of a steel plate, a zinc or zinc alloy plated steel plate, aluminum or an aluminum alloy, performing electrodeposition coating and performing treatment before the electrodeposition coating and after the film chemical conversion, using an aqueous solution that includes 1 to 100 ppm of Cu ions and that has a pH of 1 to 4.
Further, the applicant has proposed, and disclosed in Patent Document 3, a composition for post-treatment of a chemical conversion film including water, (A) a fluorometal acid anion that includes 4 or more atoms of F, 1 or more atoms of an atom selected from Ti, Zr, Hf, Si, Al, and B, 1 or more atom of an ionizable hydrogen as a selective component and/or 1 or more atom of oxygen, (B) a divalent or quadrivalent cation selected from Co, Mg, Mn, Zn, Ni, Sn, Cu, Zr, Fe, and Sr, (C) one or both of an inorganic oxyanion containing P and a phosphonate anion, and (D) a water-soluble and/or water dispersible organic polymer and/or a polymer-generating resin.
By any one of the above-noted methods, however, although the corrosion resistance and adhesion improved after coating with a zinc phosphate treatment film, the heat resistance and film adhesion was not achieved.
In a method proposed in Patent Document 4 for improving adhesion during coating by coating a metallic material, powder coating is performed after a metallic material, the surface of which has been treated with a phosphate treatment solution, is treated by using an aqueous solution containing a component consisting of one or more kinds of phenol compound derivatives having an average degree of polymerization of 2 to 50 of one or more kinds of polymerization units represented by a general formula (I), and is dried.
However, as long as a zinc phosphate treatment film is used for foundation layer treatment prior to coating, it is impossible to avoid the destruction of the film that is caused by a dehydration reaction from the crystal of a zinc phosphate film at the time of high-temperature baking, and it has not been possible to eliminate a basic cause related to heat resistance.
Moreover, although there is no language to this effect in Patent Document 4, if the above-noted method is applied to a solid lubrication coating, because the surface of a coated film is under high surface pressure, high loading, and high temperature in the environment of use after coating, breaking of the crystal of the zinc phosphate film, which is the foundation layer, occurs, and peeling away of the film might occur.
As long as a zinc phosphate treatment is used as described above, the problem of heat resistance is unavoidable.
Given the above, if the coated film is to be exposed to a high temperature during the baking of the coating or in the environment in which it is used after coating, an iron phosphate film treatment is generally employed as a foundation layer treatment prior to coating. Because it is an amorphous material, an iron phosphate film is superior in heat resistance to a zinc phosphate film. For this reason, an iron phosphate film is widely used.
However, the heat resistance and acid resistance of the iron phosphate film at a high temperature is also insufficient, and the corrosion resistance of the iron phosphate film after coating is significantly lower than that of a zinc phosphate film. For this reason, the iron phosphate film might could not withstand a severely corrosive environment.
Further, the crystals of the phosphate calcium film are also superior to the crystals of a zinc phosphate film in terms of heat resistance, and the crystals of a manganese phosphate film have excellent mechanical strength.
However, all of the cited methods are inferior to a zinc phosphate treatment as a foundation layer treatment prior to coating in terms of corrosion resistance, and there is room for improvement in terms of adhesion. Furthermore, because the film is inferior in terms of electrical conductivity, use was not possible in batteries, in electrical components, or in applications requiring an antistatic property.
Up until now, no practical metallic material wherein a metal oxide different from an underlying metal has excellent corrosion resistance and adhesion even in severe environments, such as at the high temperatures as described above, and wherein a film having electrical conductivity is formed, and a method of manufacturing the metallic material have been discovered.
Meanwhile, specific metal oxides, such as a zirconium oxide or a titanium oxide, have very superior heat resistance and chemical resistance.
The applicant has proposed (see Patent Documents 5 and 6) a composition for the surface treatment of a metal, containing a compound that contains at least one kind of metal element selected from the above-noted Ti, Zr, Hf, and Si and a compound that contains at least one element selected from Ag, Al, Cu, Fe, Mn, Mg, Ni, Co, and Zn.    Patent Document 1: Japanese Laid-Open Patent Application (JP-A) No. 52-80239    Patent Document 2: Japanese Laid-Open Patent Application JP-A No. 7-150393    Patent Document 3: Japanese Laid-Open Patent Application JP-A No. 11-6077    Patent Document 4: Japanese Laid-Open Patent Application JP-A No. 2001-9365    Patent Document 5: Pamphlet of International Publication No. 2002/103080    Patent Document 6: Japanese Laid-Open Patent Application JP-A No. 2005-264230